NAME
SQL::Abstract - Generate SQL from Perl data structures
SYNOPSIS
use SQL::Abstract;
my $sql = SQL::Abstract->new;
my($stmt, @bind) = $sql->select($table, \@fields, \%where, \@order);
my($stmt, @bind) = $sql->insert($table, \%fieldvals || \@values);
my($stmt, @bind) = $sql->update($table, \%fieldvals, \%where);
my($stmt, @bind) = $sql->delete($table, \%where);
# Then, use these in your DBI statements
my $sth = $dbh->prepare($stmt);
$sth->execute(@bind);
# Just generate the WHERE clause
my($stmt, @bind) = $sql->where(\%where, \@order);
# Return values in the same order, for hashed queries
# See PERFORMANCE section for more details
my @bind = $sql->values(\%fieldvals);
DESCRIPTION
This module was inspired by the excellent DBIx::Abstract. However, in
using that module I found that what I really wanted to do was generate
SQL, but still retain complete control over my statement handles and use
the DBI interface. So, I set out to create an abstract SQL generation
module.
While based on the concepts used by DBIx::Abstract, there are several
important differences, especially when it comes to WHERE clauses. I have
modified the concepts used to make the SQL easier to generate from Perl
data structures and, IMO, more intuitive. The underlying idea is for
this module to do what you mean, based on the data structures you
provide it. The big advantage is that you don't have to modify your code
every time your data changes, as this module figures it out.
To begin with, an SQL INSERT is as easy as just specifying a hash of
"key=value" pairs:
my %data = (
name => 'Jimbo Bobson',
phone => '123-456-7890',
address => '42 Sister Lane',
city => 'St. Louis',
state => 'Louisiana',
);
The SQL can then be generated with this:
my($stmt, @bind) = $sql->insert('people', \%data);
Which would give you something like this:
$stmt = "INSERT INTO people
(address, city, name, phone, state)
VALUES (?, ?, ?, ?, ?)";
@bind = ('42 Sister Lane', 'St. Louis', 'Jimbo Bobson',
'123-456-7890', 'Louisiana');
These are then used directly in your DBI code:
my $sth = $dbh->prepare($stmt);
$sth->execute(@bind);
In addition, you can apply SQL functions to elements of your %data by
specifying an arrayref for the given hash value. For example, if you
need to execute the Oracle "to_date" function on a value, you can say
something like this:
my %data = (
name => 'Bill',
date_entered => ["to_date(?,'MM/DD/YYYY')", "03/02/2003"],
);
The first value in the array is the actual SQL. Any other values are
optional and would be included in the bind values array. This gives you:
my($stmt, @bind) = $sql->insert('people', \%data);
$stmt = "INSERT INTO people (name, date_entered)
VALUES (?, to_date(?,'MM/DD/YYYY'))";
@bind = ('Bill', '03/02/2003');
An UPDATE is just as easy, all you change is the name of the function:
my($stmt, @bind) = $sql->update('people', \%data);
Notice that your %data isn't touched; the module will generate the
appropriately quirky SQL for you automatically. Usually you'll want to
specify a WHERE clause for your UPDATE, though, which is where handling
%where hashes comes in handy...
This module can generate pretty complicated WHERE statements easily. For
example, simple "key=value" pairs are taken to mean equality, and if you
want to see if a field is within a set of values, you can use an
arrayref. Let's say we wanted to SELECT some data based on this
criteria:
my %where = (
requestor => 'inna',
worker => ['nwiger', 'rcwe', 'sfz'],
status => { '!=', 'completed' }
);
my($stmt, @bind) = $sql->select('tickets', '*', \%where);
The above would give you something like this:
$stmt = "SELECT * FROM tickets WHERE
( requestor = ? ) AND ( status != ? )
AND ( worker = ? OR worker = ? OR worker = ? )";
@bind = ('inna', 'completed', 'nwiger', 'rcwe', 'sfz');
Which you could then use in DBI code like so:
my $sth = $dbh->prepare($stmt);
$sth->execute(@bind);
Easy, eh?
FUNCTIONS
The functions are simple. There's one for each major SQL operation, and
a constructor you use first. The arguments are specified in a similar
order to each function (table, then fields, then a where clause) to try
and simplify things.
new(option => 'value')
The "new()" function takes a list of options and values, and returns a
new SQL::Abstract object which can then be used to generate SQL through
the methods below. The options accepted are:
case
If set to 'lower', then SQL will be generated in all lowercase. By
default SQL is generated in "textbook" case meaning something like:
SELECT a_field FROM a_table WHERE some_field LIKE '%someval%'
cmp This determines what the default comparison operator is. By default
it is "=", meaning that a hash like this:
%where = (name => 'nwiger', email => 'nate@wiger.org');
Will generate SQL like this:
WHERE name = 'nwiger' AND email = 'nate@wiger.org'
However, you may want loose comparisons by default, so if you set
"cmp" to "like" you would get SQL such as:
WHERE name like 'nwiger' AND email like 'nate@wiger.org'
You can also override the comparsion on an individual basis - see
the huge section on "WHERE CLAUSES" at the bottom.
logic
This determines the default logical operator for multiple WHERE
statements in arrays. By default it is "or", meaning that a WHERE
array of the form:
@where = (
event_date => {'>=', '2/13/99'},
event_date => {'<=', '4/24/03'},
);
Will generate SQL like this:
WHERE event_date >= '2/13/99' OR event_date <= '4/24/03'
This is probably not what you want given this query, though (look at
the dates). To change the "OR" to an "AND", simply specify:
my $sql = SQL::Abstract->new(logic => 'and');
Which will change the above "WHERE" to:
WHERE event_date >= '2/13/99' AND event_date <= '4/24/03'
convert
This will automatically convert comparisons using the specified SQL
function for both column and value. This is mostly used with an
argument of "upper" or "lower", so that the SQL will have the effect
of case-insensitive "searches". For example, this:
$sql = SQL::Abstract->new(convert => 'upper');
%where = (keywords => 'MaKe iT CAse inSeNSItive');
Will turn out the following SQL:
WHERE upper(keywords) like upper('MaKe iT CAse inSeNSItive')
The conversion can be "upper()", "lower()", or any other SQL
function that can be applied symmetrically to fields (actually
SQL::Abstract does not validate this option; it will just pass
through what you specify verbatim).
bindtype
This is a kludge because many databases suck. For example, you can't
just bind values using DBI's "execute()" for Oracle "CLOB" or "BLOB"
fields. Instead, you have to use "bind_param()":
$sth->bind_param(1, 'reg data');
$sth->bind_param(2, $lots, {ora_type => ORA_CLOB});
The problem is, SQL::Abstract will normally just return a @bind
array, which loses track of which field each slot refers to. Fear
not.
If you specify "bindtype" in new, you can determine how @bind is
returned. Currently, you can specify either "normal" (default) or
"columns". If you specify "columns", you will get an array that
looks like this:
my $sql = SQL::Abstract->new(bindtype => 'columns');
my($stmt, @bind) = $sql->insert(...);
@bind = (
[ 'column1', 'value1' ],
[ 'column2', 'value2' ],
[ 'column3', 'value3' ],
);
You can then iterate through this manually, using DBI's
"bind_param()".
$sth->prepare($stmt);
my $i = 1;
for (@bind) {
my($col, $data) = @$_;
if ($col eq 'details' || $col eq 'comments') {
$sth->bind_param($i, $data, {ora_type => ORA_CLOB});
} elsif ($col eq 'image') {
$sth->bind_param($i, $data, {ora_type => ORA_BLOB});
} else {
$sth->bind_param($i, $data);
}
$i++;
}
$sth->execute; # execute without @bind now
Now, why would you still use SQL::Abstract if you have to do this
crap? Basically, the advantage is still that you don't have to care
which fields are or are not included. You could wrap that above
"for" loop in a simple sub called "bind_fields()" or something and
reuse it repeatedly. You still get a layer of abstraction over
manual SQL specification.
quote_char
This is the character that a table or column name will be quoted
with. By default this is an empty string, but you could set it to
the character "`", to generate SQL like this:
SELECT `a_field` FROM `a_table` WHERE `some_field` LIKE '%someval%'
This is useful if you have tables or columns that are reserved words
in your database's SQL dialect.
name_sep
This is the character that separates a table and column name. It is
necessary to specify this when the "quote_char" option is selected,
so that tables and column names can be individually quoted like
this:
SELECT `table`.`one_field` FROM `table` WHERE `table`.`other_field` = 1
insert($table, \@values || \%fieldvals)
This is the simplest function. You simply give it a table name and
either an arrayref of values or hashref of field/value pairs. It returns
an SQL INSERT statement and a list of bind values.
update($table, \%fieldvals, \%where)
This takes a table, hashref of field/value pairs, and an optional
hashref WHERE clause. It returns an SQL UPDATE function and a list of
bind values.
select($table, \@fields, \%where, \@order)
This takes a table, arrayref of fields (or '*'), optional hashref WHERE
clause, and optional arrayref order by, and returns the corresponding
SQL SELECT statement and list of bind values.
delete($table, \%where)
This takes a table name and optional hashref WHERE clause. It returns an
SQL DELETE statement and list of bind values.
where(\%where, \@order)
This is used to generate just the WHERE clause. For example, if you have
an arbitrary data structure and know what the rest of your SQL is going
to look like, but want an easy way to produce a WHERE clause, use this.
It returns an SQL WHERE clause and list of bind values.
values(\%data)
This just returns the values from the hash %data, in the same order that
would be returned from any of the other above queries. Using this allows
you to markedly speed up your queries if you are affecting lots of rows.
See below under the "PERFORMANCE" section.
generate($any, 'number', $of, \@data, $struct, \%types)
Warning: This is an experimental method and subject to change.
This returns arbitrarily generated SQL. It's a really basic shortcut. It
will return two different things, depending on return context:
my($stmt, @bind) = $sql->generate('create table', \$table, \@fields);
my $stmt_and_val = $sql->generate('create table', \$table, \@fields);
These would return the following:
# First calling form
$stmt = "CREATE TABLE test (?, ?)";
@bind = (field1, field2);
# Second calling form
$stmt_and_val = "CREATE TABLE test (field1, field2)";
Depending on what you're trying to do, it's up to you to choose the
correct format. In this example, the second form is what you would want.
By the same token:
$sql->generate('alter session', { nls_date_format => 'MM/YY' });
Might give you:
ALTER SESSION SET nls_date_format = 'MM/YY'
You get the idea. Strings get their case twiddled, but everything else
remains verbatim.
WHERE CLAUSES
This module uses a variation on the idea from DBIx::Abstract. It is NOT,
repeat *not* 100% compatible. The main logic of this module is that
things in arrays are OR'ed, and things in hashes are AND'ed.
The easiest way to explain is to show lots of examples. After each
%where hash shown, it is assumed you used:
my($stmt, @bind) = $sql->where(\%where);
However, note that the %where hash can be used directly in any of the
other functions as well, as described above.
So, let's get started. To begin, a simple hash:
my %where = (
user => 'nwiger',
status => 'completed'
);
Is converted to SQL "key = val" statements:
$stmt = "WHERE user = ? AND status = ?";
@bind = ('nwiger', 'completed');
One common thing I end up doing is having a list of values that a field
can be in. To do this, simply specify a list inside of an arrayref:
my %where = (
user => 'nwiger',
status => ['assigned', 'in-progress', 'pending'];
);
This simple code will create the following:
$stmt = "WHERE user = ? AND ( status = ? OR status = ? OR status = ? )";
@bind = ('nwiger', 'assigned', 'in-progress', 'pending');
If you want to specify a different type of operator for your comparison,
you can use a hashref for a given column:
my %where = (
user => 'nwiger',
status => { '!=', 'completed' }
);
Which would generate:
$stmt = "WHERE user = ? AND status != ?";
@bind = ('nwiger', 'completed');
To test against multiple values, just enclose the values in an arrayref:
status => { '!=', ['assigned', 'in-progress', 'pending'] };
Which would give you:
"WHERE status != ? OR status != ? OR status != ?"
But, this is probably not what you want in this case (look at it). So
the hashref can also contain multiple pairs, in which case it is
expanded into an "AND" of its elements:
my %where = (
user => 'nwiger',
status => { '!=', 'completed', -not_like => 'pending%' }
);
# Or more dynamically, like from a form
$where{user} = 'nwiger';
$where{status}{'!='} = 'completed';
$where{status}{'-not_like'} = 'pending%';
# Both generate this
$stmt = "WHERE user = ? AND status != ? AND status NOT LIKE ?";
@bind = ('nwiger', 'completed', 'pending%');
To get an OR instead, you can combine it with the arrayref idea:
my %where => (
user => 'nwiger',
priority => [ {'=', 2}, {'!=', 1} ]
);
Which would generate:
$stmt = "WHERE user = ? AND priority = ? OR priority != ?";
@bind = ('nwiger', '2', '1');
However, there is a subtle trap if you want to say something like this
(notice the "AND"):
WHERE priority != ? AND priority != ?
Because, in Perl you *can't* do this:
priority => { '!=', 2, '!=', 1 }
As the second "!=" key will obliterate the first. The solution is to use
the special "-modifier" form inside an arrayref:
priority => [ -and => {'!=', 2}, {'!=', 1} ]
Normally, these would be joined by "OR", but the modifier tells it to
use "AND" instead. (Hint: You can use this in conjunction with the
"logic" option to "new()" in order to change the way your queries work
by default.) Important: Note that the "-modifier" goes INSIDE the
arrayref, as an extra first element. This will NOT do what you think it
might:
priority => -and => [{'!=', 2}, {'!=', 1}] # WRONG!
Here is a quick list of equivalencies, since there is some overlap:
# Same
status => {'!=', 'completed', 'not like', 'pending%' }
status => [ -and => {'!=', 'completed'}, {'not like', 'pending%'}]
# Same
status => {'=', ['assigned', 'in-progress']}
status => [ -or => {'=', 'assigned'}, {'=', 'in-progress'}]
status => [ {'=', 'assigned'}, {'=', 'in-progress'} ]
In addition to "-and" and "-or", there is also a special "-nest"
operator which adds an additional set of parens, to create a subquery.
For example, to get something like this:
$stmt = WHERE user = ? AND ( workhrs > ? OR geo = ? )
@bind = ('nwiger', '20', 'ASIA');
You would do:
my %where = (
user => 'nwiger',
-nest => [ workhrs => {'>', 20}, geo => 'ASIA' ],
);
You can also use the hashref format to compare a list of fields using
the "IN" comparison operator, by specifying the list as an arrayref:
my %where = (
status => 'completed',
reportid => { -in => [567, 2335, 2] }
);
Which would generate:
$stmt = "WHERE status = ? AND reportid IN (?,?,?)";
@bind = ('completed', '567', '2335', '2');
You can use this same format to use other grouping functions, such as
"BETWEEN", "SOME", and so forth. For example:
my %where = (
user => 'nwiger',
completion_date => {
-not_between => ['2002-10-01', '2003-02-06']
}
);
Would give you:
WHERE user = ? AND completion_date NOT BETWEEN ( ? AND ? )
So far, we've seen how multiple conditions are joined with a top-level
"AND". We can change this by putting the different conditions we want in
hashes and then putting those hashes in an array. For example:
my @where = (
{
user => 'nwiger',
status => { -like => ['pending%', 'dispatched'] },
},
{
user => 'robot',
status => 'unassigned',
}
);
This data structure would create the following:
$stmt = "WHERE ( user = ? AND ( status LIKE ? OR status LIKE ? ) )
OR ( user = ? AND status = ? ) )";
@bind = ('nwiger', 'pending', 'dispatched', 'robot', 'unassigned');
This can be combined with the "-nest" operator to properly group SQL
statements:
my @where = (
-and => [
user => 'nwiger',
-nest => [
-and => [workhrs => {'>', 20}, geo => 'ASIA' ],
-and => [workhrs => {' 'EURO' ]
],
],
);
That would yield:
WHERE ( user = ? AND
( ( workhrs > ? AND geo = ? )
OR ( workhrs < ? AND geo = ? ) ) )
Finally, sometimes only literal SQL will do. If you want to include
literal SQL verbatim, you can specify it as a scalar reference, namely:
my $inn = 'is Not Null';
my %where = (
priority => { ' \$inn
);
This would create:
$stmt = "WHERE priority < ? AND requestor is Not Null";
@bind = ('2');
Note that in this example, you only get one bind parameter back, since
the verbatim SQL is passed as part of the statement.
Of course, just to prove a point, the above can also be accomplished
with this:
my %where = (
priority => { ' { '!=', undef },
);
TMTOWTDI.
These pages could go on for a while, since the nesting of the data
structures this module can handle are pretty much unlimited (the module
implements the "WHERE" expansion as a recursive function internally).
Your best bet is to "play around" with the module a little to see how
the data structures behave, and choose the best format for your data
based on that.
And of course, all the values above will probably be replaced with
variables gotten from forms or the command line. After all, if you knew
everything ahead of time, you wouldn't have to worry about
dynamically-generating SQL and could just hardwire it into your script.
PERFORMANCE
Thanks to some benchmarking by Mark Stosberg, it turns out that this
module is many orders of magnitude faster than using "DBIx::Abstract". I
must admit this wasn't an intentional design issue, but it's a byproduct
of the fact that you get to control your "DBI" handles yourself.
To maximize performance, use a code snippet like the following:
# prepare a statement handle using the first row
# and then reuse it for the rest of the rows
my($sth, $stmt);
for my $href (@array_of_hashrefs) {
$stmt ||= $sql->insert('table', $href);
$sth ||= $dbh->prepare($stmt);
$sth->execute($sql->values($href));
}
The reason this works is because the keys in your $href are sorted
internally by SQL::Abstract. Thus, as long as your data retains the same
structure, you only have to generate the SQL the first time around. On
subsequent queries, simply use the "values" function provided by this
module to return your values in the correct order.
FORMBUILDER
If you use my "CGI::FormBuilder" module at all, you'll hopefully really
like this part (I do, at least). Building up a complex query can be as
simple as the following:
#!/usr/bin/perl
use CGI::FormBuilder;
use SQL::Abstract;
my $form = CGI::FormBuilder->new(...);
my $sql = SQL::Abstract->new;
if ($form->submitted) {
my $field = $form->field;
my $id = delete $field->{id};
my($stmt, @bind) = $sql->update('table', $field, {id => $id});
}
Of course, you would still have to connect using "DBI" to run the query,
but the point is that if you make your form look like your table, the
actual query script can be extremely simplistic.
If you're REALLY lazy (I am), check out "HTML::QuickTable" for a fast
interface to returning and formatting data. I frequently use these three
modules together to write complex database query apps in under 50 lines.
NOTES
There is not (yet) any explicit support for SQL compound logic
statements like "AND NOT". Instead, just do the de Morgan's law
transformations yourself. For example, this:
"lname LIKE '%son%' AND NOT ( age < 10 OR age > 20 )"
Becomes:
"lname LIKE '%son%' AND ( age >= 10 AND age <= 20 )"
With the corresponding %where hash:
%where = (
lname => {like => '%son%'},
age => [-and => {'>=', 10}, {'<=', 20}],
);
Again, remember that the "-and" goes *inside* the arrayref.
ACKNOWLEDGEMENTS
There are a number of individuals that have really helped out with this
module. Unfortunately, most of them submitted bugs via CPAN so I have no
idea who they are! But the people I do know are:
Mark Stosberg (benchmarking)
Chas Owens (initial "IN" operator support)
Philip Collins (per-field SQL functions)
Eric Kolve (hashref "AND" support)
Mike Fragassi (enhancements to "BETWEEN" and "LIKE")
Dan Kubb (support for "quote_char" and "name_sep")
Matt Trout (DBIx::Class support)
Thanks!
BUGS
If found, please DO NOT submit anything via "rt.cpan.org" - that just
causes me a ton of work. Email me a patch (or script demonstrating the
problem) to the below address, and include the VERSION you're using.
SEE ALSO
DBIx::Abstract, DBI, CGI::FormBuilder, HTML::QuickTable
AUTHOR
Copyright (c) 2001-2006 Nathan Wiger . All Rights
Reserved.
For support, your best bet is to try the "DBIx::Class" users mailing
list. While not an official support venue, "DBIx::Class" makes heavy use
of "SQL::Abstract", and as such list members there are very familiar
with how to create queries.
This module is free software; you may copy this under the terms of the
GNU General Public License, or the Artistic License, copies of which
should have accompanied your Perl kit.